I'm currently developing a long term data logger device based on an RFduino/RTC/PressureSensor.I already completed the logging functions for writing to SD card.

Now, i want to enable the device to transfer the logfile to a (Android) smartphone.

Sending Data via RFduinoBLE.send is already working.

What i want to do now, is making a reliable transfer service.The Rfduino should send the data in packets, along with a number to identify the packet.The Phone sould answer with an ACK to request the next packet or NACK to request resending the current packet.

I got that handshake already working, simulated over Serial Monitor.

What i need to know is:

How does the send function form the transmitted GATT packages?How many Bytes can it transfer in one GATT Package?Is it possible to custom make the Package? (for setting up a proper Package format)